I The long-term objective of this proposal is to understand the underlying molecular basis of maternal mRNA translation in early mammalian development. Specific mRNAs encoding proteins such as cyclin B and mos are translationally activated in maturing mouse oocytes by the process of cytoplasmic polyadenylation. Polyadenylation in turn is controlled by short elements that reside in the 3' untranslated regions of the mRNAs, and by the proteins that interact with these elements. The key factor necessary for polyadenylation is CPEB. A knockout of the CPEB gene results in the cessation of oogenesis at pachytene and the prevention of synaptonemal complex formation. CPEB activity is dependent upon single site phosphorylation catalyzed by <\urora, a protein kinase. We propose to investigate how Aurora is activated in mouse oocytes, and whether a phosphatase acts on phosphorylated CPEB to inactivate it at later times of oogenesis. We also propose to nvestigate cytoplasmic polyadenylation in the fertilized egg, and to determine the mRNAs that undergo this process at this time. We further propose to investigate the functions of two other CPEB-like proteins, at least one of which is present in oocytes as well as fertilized eggs. Finally, we propose to characterize maskin, a PEB-interacting factor that is key to linking polyadenylation to translational activation. With these proposed experiments, we will assess not only the mechanism of mammalian maternal mRNA is translation, but also will further investigate its clear importance for early development. Regulated mRNA translation is clearly important for the viability of all metazoans in which it has been examined. These proposed studies focus on early development, and consequently the results obtained will have ramifications for fertility and human development.